Zhong Zhong and Hua Hua, a pair of long-tailed macaque female monkeys living in China, are 49 and 51 days old respectively, but genetically they are completely identical.

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Scientists affiliated with the Chinese Academy of Sciences reported on Wednesday that they had successfully cloned the monkeys in an experiment that merged monkey fetal cells with an egg cell that had its own genetic material removed. While scientists have cloned a number of other species, the milestone has been hailed as a breakthrough, marking the first time any sort of primate has been cloned using a technique that in 1996 also produced Dolly the Sheep.

Additional clones were created from adult monkeys, and both died quickly after being born, but more are still gestating in surrogate mothers. In theory, Stat reports, the same technique—very similar to the one used to clone Dolly the Sheep in 1996—sets the stage for cloning humans, though the scientists say they have no plans to do so.

Cloned animals are, by definition, genetically identical, so they could potentially be used to study the effects of drugs, diets, or other factors without worrying about genetic differences. Or genetic modification techniques like Crispr could be used to generate clones that are identical but for a few genes that scientists want to study.

Monkeys are similar to humans in many ways, especially compared to animals like lab rats, so they could be useful in studying certain diseases, though working with them can be expensive and raise ethical issues that aren’t considered with simpler creatures like rodents.

In fact, U.S. labs have been reducing their use of primates in medical research. And the notion of cloning humans has stoked another set of weighty ethical concerns before. Given current safety issues, the Chinese technique “is still a long way from producing human babies,” the New York Times’ Gina Kolata writes. But the study has just brought us a step closer to that possibility, and to the resurgence of a difficult ethical debate.

And for now, it’s also possibly given us a useful new approach to medical research, and at least a couple of adorable monkeys.